Watches 101: Movements

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The iconic Zenith El Primero caliber 3019 PHC manually-wound movement

Hey all, I wanted to start a new series! Obviously, many people here are already extremely knowledgeable about watches, but one of the joys of the hobby is spreading knowledge. Please let me know in comments if there's anything that the community would like to learn about. I definitely don't know everything (or even more than many people), but we have such a breadth of knowledge in the community that it would be a waste to not share! For this first installment, I'd like to talk about the (almost literal) heart and soul of every watch, the movement.
WHAT IS A MOVEMENT?
The movement of a watch refers to all of the internal workings that keep it running and telling the time. The movement includes, but is not limited to, components that store power to drive the rest of the movement, gears that turn the hands and run the complications, jewels/screws/plates that hold the whole thing together, etc.
GLOSSARY OF TERMS
Before we get too much into the nitty gritty of things, I'd like to go over some terms that you'll hear a lot when referring to watch movements.

Caliber: The specific internal movement of the watch or clock. The word is used to designate individual models of movements, and the format is typically “[movement maker] caliber [model number]” (e.g. Miyota caliber 9015 or simply Miyota 9015).

In-house: The movement contained in the watch is made by the same manufacturer as the watch itself. Sometimes seen as more desirable due to exclusivity and tradition, but this is a topic of hot debate amongst enthusiasts.

Jewels: Typically made of synthetic corundum (the same sapphire used in many crystals), these are inserted at pivot points in the movement. Sapphire has beneficial properties of being extremely hard (second only to diamond), which reduces frictional wear due to moving parts.

Wheels & pinions: The gears that make up the movement. Wheels are large and pinions are smaller.

Mainspring: In a mechanical movement, the mainspring holds the kinetic energy which is to be transferred through the movement to tell the time. Housed within the barrel.

Escapement: Made up of the pallet fork, escape wheel, balance wheel, and hairspring, the escapement regulates the speed at which kinetic energy is released from the mainspring. Without the escapement, the coiled mainspring would simply release all of its tension at once. The escapement allows the watch to tell proper time. Each time the balance wheel oscillates back or forth, the second hand sweeps forward slightly.

Mainplate & bridges: Metal pieces that hold parts of the movement in place. The mainplate is the largest foundational piece of each movement. Bridges are smaller and attached to the mainplate with screws.

Rotor: A weighted piece attached to the winding works and allowed to rotate freely around an axle. Constantly drawn down by gravity, the motion of the wearer or watch winder causes the rotor to swing and wind the watch.

Keyless works: Prior to technological advancements, pocketwatches were wound by a key inserted into a hole to directly wind the mainspring. The keyless works was a mechanism designed to conveniently combine winding and time-setting through the winding stem, which can be manipulated via the crown of the watch.

Motion works: The gear train that drives the hands of the watch.

Center wheel: Carries the minute hand, typically in the center of the watch. Rotates once an hour. The gear train then converts the rotational speed of the minute hand to turn the second and hour hands at the appropriate speed.

Third wheel: Converts the rotational speed of the center wheel to make it possible to tell seconds. Connects the center and fourth wheels.

Fourth wheel: Carries the second hand on dials that feature a seconds subdial. Rotates once a minute.

VPH, BPH, Hz, Frequency: These terms all refer to the way of telling how many “beats”, or oscillations, the balance wheel is making over a period of time. VPH/BPH stands for vibrations/beats per hour. To convert frequency from vph to Hz, you would divide by 60 (hours to minutes), 60 again (minutes to seconds), then two (two vibrations per second). Many common frequencies are 18000 (2.5 Hz), 21600 (3 Hz), or 28800 (4 Hz). Hi-beat movements may go up to 36000 (5 Hz), 72000 (10 Hz), or higher. Higher frequency means that the second hand will tick in smaller subdivisions, which can sometimes mean better precision. This topic is debated lightly, but is important in chronographs in which the subdivisions within a second may be important.

Complications: Any function in a movement beyond the simple display of hours and minutes. Technically, having a seconds hand attached to the same pinion as the hour and minute hands constitutes a complication; typically, the seconds hand would be attached directly to the fourth wheel and displayed in a subdial. Common complications include, but are not limited to, calendar displays (date windows included), chronographs (stopwatch functionality), and hacking seconds (stopping the seconds hand from moving while setting the time).

Finishing: Many different techniques applied to parts of the movement that will make it look more aesthetically pleasing. Different techniques of finishing also have added benefits of reducing wear on the movement. Finishing techniques constitute a whole other rabbit hole that we can go into on a different day.

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MECHANICAL VS QUARTZ (the basics)
The different types of movement all have to do with how power is stored and released to regulate the movement of the hands. Here's a handy little Venn-diagram I slapped together, the two main families of movements are mechanical and quartz:

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Mechanical movements are just that: mechanical. Mechanical movements store kinetic energy into a mainspring, which then releases the energy through a series of gears and ultimately through a regulatory hairspring, which dictates how quickly the hands of the watch move. Within the mechanical circle, you'll notice a smaller subset reading "automatic". Instead of winding the movement through the crown, automatic movements utilize the power of gravity with a weighted rotor attached to the winding mechanism. As the watch is worn and moved around, the rotor winds power into the movement.

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Here you can see the difference between a manual wind movement (left, Lemania CH27) and automatic movement (right, Rolex 4030). The semicircle at the top of the automatic movement is the weighted rotor, which is absent on the manual wind.

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Some automatic movements, such as this Laurent Ferrier Galet Micro-Rotor, have a smaller weighted rotor (as shown at 3 o'clock of this photo) instead of the full semicircle. These rotors are a little less efficient at winding the mainspring, but look darned cool.

Here's a nifty little video that does a great job detailing how a mechanical movement works:

Quartz movements, on the other hand, typically use a small battery to supply power and run an electrical current through a precisely cut quartz crystal to regulate the movement of the hands.
Quartz was chosen because of its extremely precise oscillating frequency; when subjected to electrical charge, it will bend and flex. If cut to the right size and shape, it will resonate at 32768 Hz (235,929,600 vph). This number is significant for two reasons. First, it is too high of a frequency to be distinguishable to the human ear (imagine if your quartz watch whined while you wore it, that would get tiring extremely quickly), and it is a power of two. As a result, a small digital counter can easily subdivide the frequency to isolate one second digital pulses.

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The ubiquitous Ronda 715 quartz movement

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Rolex 5035 Oysterquartz movement

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F.P. Journe Caliber 1210 quartz movement. Journe's decision to make a quartz movement is seen as controversial by some, as this watch is over $10,000. That being said, the technical considerations that went into this watch are astounding; the bridges and plates are made of rose gold, and the hands stop after thirty minutes of stillness to save battery. The microprocessor will continue to run and the hands will sync up as soon as the watch is moved.

You can typically tell the difference between a mechanical and quartz movement by how the seconds hand moves. A seconds hand on a quartz watch will tick discrete seconds, jumping from one second to the next. Meanwhile, the seconds hand on a mechanical watch will “sweep” along. It is still ticking, just in smaller and quicker increments which contribute to a smooth glide around the dial. This is muddied a bit when you get into complications and haute-horology, some manufacturers (such as Jaeger-LeCoultre) make what is called a deadbeat or “true” second hand. These are purely mechanical watches, but the escapement and balance wheel is made in such a way that will cause the second hand to tick once a second. Whether this complication is enjoyed for precision or for whimsy is up to the owner of the watch.
The hybrid movements are a very interesting section of watchmaking. These are movements that will combine aspects of both mechanical and quartz watches. Seiko, for instance, makes many “mecha-quartz” and kinetic movements. Mecha-quartz simply refers to a watch that uses a quartz movement for time-telling but a mechanical chronograph. Kinetic movements have a weighted rotor that winds power into the watch but uses a quartz timekeeping package to drive the hands.
Another interesting movement is Grand Seiko’s Spring Drive. The Spring Drive uses a weighted rotor to wind power into a mainspring, just like a mechanical watch. It also generates an electrical current to regulate timekeeping, just like a quartz watch. However, the Spring Drive movement uses this electrical current to exert a magnetic braking force on a constantly spinning “drive wheel” (in place of the traditional escapement). As a result, the seconds hand of a Spring Drive will truly sweep, instead of the tiny ticks of a mechanical watch. It’s not quite mechanical and not quite quartz, it occupies a space all on its own.

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Grand Seiko Spring Drive Caliber 9R65. The weighted rotor is up top, and you can see the glide wheel escapement in gold at around 7 o'clock in this photo.

TECHNOLOGY AND ADVANCEMENTS
Even though watchmaking is by now an ancient and storied industry, new innovations are constantly being developed and implemented. Quartz movements, in fact, were a result of technological advancements in the early 20th century and started becoming popular in the 1970's and 1980's during a period referred to as the “quartz crisis”. Many manufacturers saw quartz movements as the way of the future and started pouring all of their resources and time to develop the technology. As a result, many long-standing manufacturers went out of business as the demand for mechanical watches dwindled. Recently, we’ve started to see a renaissance of sorts as people begin to appreciate the tradition and artisanal workmanship of mechanical movements.
New materials and manufacturing techniques are also starting to be incorporated heavily into movement manufacturing. Silicon in particular has seen an uptick in its use in escapements, springs, and levers; it is durable, lightweight, anti-magnetic, and resistant to permanent deformation, which makes it a logical material for use in parts that must move around a lot. Some notable watches that show the potential of silicon include the Ulysse Nardin Freak and the Parmigiani Fleurier Senfine Concept (boasting a SEVENTY DAY power reserve). Other industry leaders such as Rolex and Patek Philippe are also gradually incorporating more and more silicon into their movements. With all these giants pushing the envelope where they can, I’m personally interested to see where the industry moves next!
WHICH IS BETTER?
And here, we come to a debate that will likely get you heated replies from enthusiasts, casual watch wearers, and snobs alike. Objectively, a quartz watch will probably be more accurate and convenient than a mechanical watch. Batteries these days have come a long way; they generally have lifetimes of a couple of years. If you want to preserve a quartz battery, you can even pull the crown out when you store the watch for an extended period of time. This will stop the movement and extend the battery's life, but has a drawback of exposing the movement to more atmospheric stress.
So, why do many enthusiasts love mechanical watches? That's a question to be answered by each individual, everyone gets into it for a different reason. For me personally, it's the workmanship that goes into putting hundreds of tiny moving pieces into something so precisely engineered and accurate to track the passage of time. There's something about mechanical movements that transcends the purely functional and becomes artistic in a way.
I'm sure everybody who has fallen into this lifestyle has a million different reasons why it attracts them so strongly. Of course, there are those who are perfectly happy wearing a quartz watch and thinking nothing of it (or even wearing no watch at all); at the end of the day, this is a hobby and meant to bring you enjoyment.
REFERENCES AND FURTHER READING
https://www.hodinkee.com/watch101
https://www.nist.gov/pml/walk-through-time-revolution-timekeeping
https://tf.nist.gov/general/pdf/2276.pdf

It is a nice article, but I will be the guy to pick at some nits.
re: Kinetic movements. The keystones of Kinetic is that it uses a normal quartz movement, but the battery (or storage capacitor originally) is recharged by the motion of the rotor. It is not "winding" anything. In this sense it can be thought of more closely related to solar-powered movements, not really mechanical. Personally I do not consider them in the hybrid category at all.
re: Seiko SpringDrive. This is a hybrid that is closer to 85% mechanical automatic. It uses a mainspring that must be wound-up to move the gear-train that moves the hands. The difference is that the rotor also charges up a storage capacitor similar to a Kinetic, and that in turn powers the electronic module that replaces the balance of a purely mechanical movement. So the module applies the braking-force instead of a balance-wheel-and-pawl-system. There is no electric stepper-motor providing the motion, it is a wound-up spring doing that.
I am not sure what you consider to be "advancements in the early 20th century" that led directly to quartz movements. Really it took the invention of digital circuitry more in the middle of the century, then a pulse-counter circuit, a quartz-regulated oscillator, and the stepper-motor. Then it all had to be miniaturized with integrated circuits. Quartz watches at the beginning were technological marvels and were very expensive. Think about how Seiko markets SpringDrive today.
There were stepping-stones to the quartz movement. In the 1950's there were some watches with an electric motor and a battery. They were considered a convenience as you did not have to remember to wind it daily. Not really any more accurate. In the early 1960's Bulova invented the Accutron movement. Accutron was a more accurate electrically-powered movement because it used an electrically-driven vibrating tuning-fork to actually push motion through a gear-train and to the hands. The vibration could be tuned to stay accurate with less than 6 seconds a month of variation. It was this higher-end market that quartz watches were invented to compete in, and eventually dominate.

Thanks for the informed input! I didn't want to go too far into the details of quartz development in an overview, but perhaps I should have. I can incorporate some of the other details that you mentioned regarding the kinetic movements; I admittedly didn't know as much about them as I thought.

All good. There are many myths regarding Kinetic and SpringDrive that spread around from people who don't really understand electronics or mechanics that well. They just keep getting repeated and other people trust it. My education is in electronics and I have worked with mechanical devices over a lifetime. Once I read more about the movements, they do not mystify me.

Great write up! I have a question regarding quality of mechanical/automatic watches. I own 2 pocket watches that are both over one hundred years old and each only requires a cleaning once every couple of years to keep accurate time. In today’s lineup of new mechanical movements, do I have to sell my car to buy a mech watch that will last a lifetime(with proper care & treatment of course) or can I trust a sub $500 watch given that many watches over a wide money span use the same movements?

Not at all! Many mechanical movements are built to last these days. Just as you can buy a $70 kitchen knife and keep it for an extended period of time with regular maintenance, so too can you buy a mechanical watch that won't break the bank and keep it going for life.
It's a bit hard to tell how long modern movements may last, as many of them have not been around for long enough to transcend generations. I know of many people who have been wearing the same watch with a basic ETA or Miyota movement for years and years. With many watches now using the same movements, what I would expect is that the movements will become easier and cheaper to service. Worst case scenario, some manufacturers now will completely replace a movement instead of repairing (could be good or bad depending on how you feel about this practice).

The question that is more important to ask is how much you are willing to spend on a service. For many high end watches, service costs upwards of $500 are not unheard of. Even a basic movement like an ETA 2824 might be around $100 or more to fully service; if your watch originally cost $200 or so, would that price be too much?

Thanks Vincent. Nicely written and in plain English so that even someone like me who is new to liking/loving watches can learn and understand more about them and how they work. Good length too, and not too technical. One small correction in the Which Is Better? section - I think you meant batteries generally have lifetimes of a few years, rather than months.

I got started writing this and realized it'd be a lot longer than I initially anticipated. Let me know in the comments if you enjoyed the format, found it interesting, or if there's anything else you'd like me to research and write up.